In a medium saucepan, whisk together fresh lemon juice, zest, egg yolks, granulated sugar, and a pinch of salt. Cook over medium-low heat for 20–25 minutes, stirring constantly until thickened. Remove from heat and whisk in cold, cubed unsalted butter until smooth. Refrigerate until firm.

In a large mixing bowl, whisk together all-purpose flour, baking powder, and a pinch of salt. In a separate bowl, cream softened butter and granulated sugar until light and fluffy. Add an egg yolk, vanilla extract, and lemon zest, mixing until integrated. Gradually fold dry ingredients into wet until just combined. Chill dough in the refrigerator for 1 hour.

Preheat oven to 350°F (175°C). Line baking sheet with parchment paper. Scoop out 1-inch balls of dough and place on prepared sheet, pressing a shallow well in each. Bake for about 10 minutes until edges are golden and centers are soft.

Fill warm wells with chilled lemon curd, allowing it to melt slightly. Dust with powdered sugar if desired. Let cool on baking sheet for a few minutes before transferring to a wire rack.